Effect of Ta thickness on the perpendicular magnetic anisotropy in MgO/CoFeB/Ta/[Co/Pd]n structures

Abstract

We studied the effect of a thin Ta layer on the perpendicular magnetic anisotropy (PMA) of composite FM1/Ta/FM2 magnetic structures, where FM1 represents the subsystem MgO/CoFeB, and FM2 denotes a [Co/Pd]6 multilayer. The stack without Ta spacer layer shows no PMA. Once a Ta layer is inserted between the thin CoFeB layer and the [Co/Pd]6 multilayer, PMA is observed. The perpendicular magnetization loops show squareness ratios close to unity, indicating the presence of almost complete perpendicular anisotropy. These hysteresis loops also show sharp switching characteristics, indicating that the MgO/CoFeB bilayer and the [Co/Pd]6 multilayer are ferromagnetically coupled together. The coercive field Hc of the composite structure increases as Ta thickness increases. Our results show that Ta layer is essential for integrating MgO/CoFeB and [Co/Pd]6 into a composite magnetic structure with perpendicular anisotropy.

MAGNETIC PROPERTIES AND DOMAIN STRUCTURE OF CoFeB/Pd MULTILAYERS WITH PERPENDICULAR MAGNETIC ANISOTROPY

“…These multilayers play a key role in spintronics devices [1][2][3] and high density magnetic recording media. Thus, the investigations of the PMA multilayers have been paid much attention [4][5][6][7][8].…”

Buffer influence on magnetic dead layer, critical current, and thermal stability in magnetic tunnel junctions with perpendicular magnetic anisotropy

“…The latter is particularly interesting due to the advantageous features exhibited by MTJs which include low critical switching current density, good thermal stability, low power consumption and the ability to scale down the junction size [9][10][11][12]. In general, as the PMA can be affected by the MTJ layer structure [14][15][16][17][18], these properties can also be modified significantly, creating an opportunity for further improvement of the magnetic memory technology based on MTJs. Recently, a lot of attention has been paid to layer thickness and buffer material problems in FeCoB/MgO systems [15][16][17][18][19], which are widely used to achieve large Tunneling Magnetoresistance (TMR) values [10,15,20].…”

“…In general, as the PMA can be affected by the MTJ layer structure [14][15][16][17][18], these properties can also be modified significantly, creating an opportunity for further improvement of the magnetic memory technology based on MTJs. Recently, a lot of attention has been paid to layer thickness and buffer material problems in FeCoB/MgO systems [15][16][17][18][19], which are widely used to achieve large Tunneling Magnetoresistance (TMR) values [10,15,20]. Different buffer layer textures may influence the roughness and thus the electrical and magnetic properties of the samples [21][22][23], affecting the parameters which are crucial in the context of magnetic memory.…”

Optimization of top-pinned perpendicular anisotropy tunnel junctions through Ta insertion

“…Early approaches to obtain high PMA reference layers relied on rare-earth-transition-metal alloys 5) or L1 0 alloys, 6) but it was soon realized that a single layer cannot fulfill all requirements; as a result, the REF layers are now much more complex systems. A common feature is the use of a Ta=FeCoB=MgO bcc spin-polarizing layer (PL) [7][8][9][10][11][12][13][14][15] with additional layers organized globally as a synthetic ferrimagnet that minimizes the generation of stray fields that would perturb the free layer (FL) operation.…”